A device 100 (FIG. 1a) equipped with an electromechanical actuator 102 for a valve 110 comprises, in general, springs 102 and 103 and electromagnets 106 and 108 for controlling the position of the valve 110 by means of electric signals controlled by a processor 101.
More specifically, these electric signals comprise currents intended to generate magnetic fields that permit the valve 110 to be displaced or maintained in a given position.
The rod of the valve 110 is pressed for this purpose against the rod 112 of a magnetic plate 114 that is movable between the two electromagnets 106 and 108 in order for the plate to be displaced or maintained in such a position that the valve 110 is opened (FIG. 1a), permitting the admission of gas into the cylinder 117, or closed (FIG. 1b), blocking the admission of gas into the cylinder 117, depending on the magnetic fields to which the plate is subjected.
For example, the displacement of the valve 110 into an open position (FIG. 1a) is achieved by controlling an attracting current Iat in the coil 107 of the electromagnet 106, which will then attract the plate 114 by means of a magnetic field Hat, the rod 112 of the plate displacing the valve 110 into the open position.
The actuator 102 may also be equipped with magnets 118 (electromagnet 108) and 116 (electromagnet 106), which latter is shown in FIG. 1b, the magnets being intended to optimize the operation of the device, especially by reducing the operating noise of the actuator and the energy necessary for the attraction and the maintenance of the plate 114 in a switched position.
Each magnet is located for this purpose on an electromagnet such that its magnetic field Hai holds the mobile plate against the electromagnet, as is shown in FIG. 1a. 
Thus, the magnetic field Hai of the magnet participates in the attraction of the plate, and this magnetic field Hai consequently permits the plate 114 to be held against an electromagnet with a reduced or even zero holding current.
However, the use of a magnet 118 (FIG. 1b) has the drawback that when the plate 114 must move away from an electromagnet 108 equipped with the magnet 118 to control a switching of the valve 110, the magnetic field Hai generated by that magnet exerts a restoring force, which opposes this moving away, which interferes with the control of the valve 110, slowing down its displacement and completely preventing its transition.
To limit this drawback, it is known that a current Idé can be controlled, which is called a defluxing current and is intended to generate a magnetic field Hdé that partially or completely compensates the magnetic field Hai generated by the magnet 118 of the electromagnet 108 such that the plate 114 is now subject to a weaker restoring force.
It should be noted that the defluxing current Idé has an opposite direction in the coils of an electromagnet compared with the direction of the attracting current Iat.
The effect of the defluxing current Idé on a valve switching will be described in detail below on the basis of FIG. 2a, which shows the location (ordinate 200, in mm) of the magnetic plate 114 between the two electromagnets 106 and 108 as a function of the time (abscissa 202, in msec), and of FIG. 2b, which shows the intensity and the duration of the defluxing current Idé (ordinate 204) flowing in the coil 109 of the electromagnet 108 as a function of the same chronology as in FIG. 2a (abscissa 202, in msec).
By comparing the rapidity of transition of the plate 114 from the electromagnet 108 (200108) to the electromagnet 106 (200106) for defluxing currents Idé1 and Idé2 of distinct intensity and duration, it is seen that the rapidity of the transition increases with increasing intensity and duration of the defluxing current.
Empirically, the transition shown by curve C1 drawn in dotted line using a current Idé1 of a duration and intensity lower than those of current Idé2 requires a longer time than the transition shown by curve C2 drawn in solid line, which is associated with this current Idé2.
Consequently, a process control strategy should be defined in order to determine the defluxing current Idé furnishing the required valve control.
However, this defluxing current Idé also must be determined taking into account the energy consumption of the actuator in order to optimize this energy consumption.
Thus, as is shown in FIG. 3, the energy required by the defluxing current, shown on the abscissa 302, affects the electric energy consumption of the actuator (ordinate 304) such that an energy optimum 306 can be obtained for a switching time Δt1 (FIG. 4, ordinate 400, showing the switching time) longer than the minimum switching time Δt0, which said minimum switching time Δt0 requires a higher electric energy.
The deceleration of the valve to obtain a longer switching time than the optimum switching time Δt1 also requires more energy.
This is why it is known that the intensity of the defluxing current Idé can be reduced as the speed decreases in order to optimize the controlled defluxing current.
Thus, the current consumption of the device is reduced at low engine speed, whereas the prolongation of the switching time of the valve can correspond to the longest engine cycle of a low-speed engine.